Method and apparatus for heat treating metal



www

@wml

METHOD AND APPARATUS FOR HEAT TREATING METAL Filed NOV. 15, 1962 Aug-25, 1964 D. P. wHlTAcRE 2 Sheets-Sheet 1 INVENTOR 00A/ALD WH/TACRE A7TO/2NE Y Aug. 25, 1964 D. P. wHlTAcRE 3,146,336

METHOD AND APPARATUS FOR HEAT TREATING METAL Filed NOV. 15, 1962 2Sheets-Sheet 2 'Iz ,v4 l-l w I I 4 life l70A /70 l70B 76 l Q l 78 lELEC; l IO/i TRODE ffy-5 66 kl r* f x 7g /SO /82 lj ELEC- /`O ELEC,-TRODE. g TRODE T-:r L/t POWER LJ SUPPLY g 90 lo 13.4.6 f g l ELEC- O4 l,|02

TRODF. lo

m0,; f ELE@- l p TRODE POWER ELEC" l i Lijn4A (O6 Fig, i 00A/Amp WH/rAc/Qf:

BY uw uw A WOR/VE Y United States Patent Office 3,146,336 Patented Aug.25, 1964 3,146,336 METHOD AND APPARATUS FOR HEAT TREATING METAL DonaldP. Whitacre, Alhambra, Calif. (5649 Alhambra Ave., Los Angeles 32,Calif.), assignor, by mesne assignments, to Donald P. Whitacre andJoseph E.

Harling Filed Nov. 15, 1962, Ser. No. 237,909 23 Claims. (Cl. 219-121)This invention relates to a method and apparatus for cleaning thesurface of metal and, more particularly to improvements therein.

This application is a continuation in part of an application for aMethod and Apparatus for Cleaning Metal, Serial No. 97,498, filed March22, 1961, and assigned to a common assignee, now abandoned.

After metal such as steel wire or rod stock has been rolled or otherwisetreated at a mill, there remains the problem of removing the scale whichis on its surface. Considerable effort has been expended in trying tofind the best way for most expeditiously and economically removing thisscale. A favored arrangement at present appears to be to employ tanksfull of acid through which the stock is drawn. It will be appreciatedthat concomitant with the acid tanks there must be established expensiveventilation equipment and other protective devices for human beings, asWell as facilities for removing the acid from the surface of the stock.Thus, although such an arrangement is being used, it does not appear tobe completely satisfactory.

An object of this invention is the provision of a new and improvedmethod and means for removing scale from the surface of metal.

Another object of this invention is the provision of a method and'meansfor removing scale from the surface of metal which does not require theuse of acids.

Still another object of the present invention is the provision of aninexpensive and effective method and means for cleaning and/ orheat-treating metal.

Yet another object of the present invention is the provision of anarrangement for removing scale from wire stock which operates morerapidly than previously known methods.

Still another object of this invention is the provision of a novelmethod and means for establishing and maintaining a rotating plasma arcwhile one of the electrodes is moved.

These and other objects of the invention are achieved in an arrangementwherein there is established a scavenging station through which theelongated conductive stock, such as rod or wire stock, is passed. Atsuch scavenging station there is established one or more rotating plasmaarcs which terminate at the surface of the conductive stock and act toremove the scale from the surface of the stock.

The novel features that are considered characteristic of this inventionare set forth with particularity in the appended claims. The inventionitself, both as to its organization and method of operation, as well asadditional objects and advantages thereof, will best be understood fromthe following description when read in connection with the accompanyingdrawings.

FIGURE l illustrates an embodiment of this invention.

FIGURE 2 illustrates an embodiment of this invention using adjustableroller electrodes as well as a single movable plasma electrode.

FIGURE 3 shows an embodiment of the invention using two electrodes.

FIGURE 4A and FIGURE 4B show embodiments of the invention in a verticalloop configuration.

FIGURE 5 illustrates an embodiment of the invention including aquenching step.

The phenomenon comprising an arc discharge through a gas is well known.It is known as a plasma arc when the gas becomes sufficiently ionized tobecome electrically conductive and conduct the arc currents flowing inthe ionized gas. Arrangements for causing such arc discharge are wellknown and simply comprise applying a voltage across two electrodes,which are spaced from one another, to cause a discharge through a gaswhich is provided between the electrodes. According to the presentinvention, such an arc is established between an electrode and theconductive stock which serves as the other electrode and caused torotate by the presence of a magnetic field. The arc provides anelectronic and ionic bombardment of the surface of the conductive stock,which effectively blasts the scale away and thus scavenges the stock. a

Besides exhibiting the property of being able to conduct electricalcurrent, a plasma arc also provides an elevated temperature on the orderof thousands of degrees Fahrenheit. Because the stock moves through thearc rapidly, only a very thin surface layer is exposed to the heatingeffect, but its rise is insufficient to cause oxidation. However, byslowing the speed of travel of the stock through the arc, advantage ofthe heating property of the arc may be taken in accordance with thisinvention for the purpose of heating the surface of the stocksufficiently to burn away any scale which is acquired in the process ofthe stock fabrication, such as by hot rolling. In this instance, theconductive stock must be kept in an inert atmosphere until it can cooldown to a temperature at which its surface will not reoxidize.Alternatively, the heating effect may be employed for elevating thetemperature of the stock sufficiently to enable heat treatment thereof.

Although arrangements for striking and maintaining a plasma arc in thepresence of stationary electrodes is well known, problems arise where itis desired to strike and maintain the arc stationary while one of theelectrodes, which here is the elongated conductive stock sought to betreated, is moved. The plasma arc exhibits what is known as a viscous orcathode effectthat is, as the electrode is moved, the arc tends to staywith the spot at which it is ignited and thus tends to elongate in thedirection of motion and thereby becomes extinguished. Accordingly, itwas necessary to find an arrangement for overcoming this viscous effect.

Another problem which presents itself is that the plasma arc is affectedby a magnetic field. Thus, if an arc is struck between an electrode andan elongated wire serving as the other electrode, then a magnetic fieldwill exist due to current flowing in the elongated wire which can movethe arc and thereby lengthen it sufficiently to be extinguished, thisphenomenon being known as the magnetic pressure effect. Other effectssuch as the entropy effect and the cyclotron effect also causedisplacement of the arc by virtue of applied magnetic fields interactingwith the fields produced at the surfaces of the arc and the fields, dueto the ow of current in the electrodes which, to a degree, can adverselyaffect the stability of the arc. Thus, it was necessary to find anarrangement which could maintain the plasma arc on the moving stock,despite the presence of these adverse effects.

Reference is now made to the drawing FIG. 1, wherein there may be seenan arrangement in accordance with this invention for applying a plasmaarc to the surface of an elongated conductor such as wire stock. Theresultant heat can scavenge the surface of the wire stock to effectuatecleansing or may be used for heat treatment if desired. The wire stockis supported by conductive rollers 12, 14, 16, and as viewed on thedrawing, is moved through these rollers by being wound up on a drum 18,which is driven by a motor, not shown. The arrangement for moving thestock may be any of those well known in the art. The rollers may bedriven and thus move the stock.

In being pulled through the rollers, the conductive metal stock also ispulled through what may be termed as a scavenging location. Two areshown in the drawing. However, it will be understood that as few or asmany of these may be employed as are required for performing the desiredoperation.

Considering the first location at which a rotating plasma arc isestablished, the mechanism for creating this arc includes a cylindricalelectrode 20, shown in section. This electrode actually comprises ametal holder A, preferably of steel, having a cylindrical opening inwhich there is inserted a copper cylinder 20B. Provision is made forcooling the copper cylinder, which is the actual operating electrode, byhaving an aperture 22 in the steel cylinder which abuts the coppercylinder and through which cooling liquid is caused to flow. The coppercylinder has a central aperture through which the stock to be treatedmay pass. This central aperture may be described as having threeportions: a small-diameter portion 24A, a transition portion 24B, and alarge-diameter portion 24C. The small-diameter portion extends inwardfrom the downstream side of the electrode 20B; the largediameter portionextends inward from the upstream side of the electrode 20B; and thetransition portion 24B exextends between these two portions. It shouldbe noted further that the large-diameter portion extends for a longerdistance than does the small diameter portion.

Positioned adjacent the upstream side of the electrode 20 is a magnet26, shown in section, which includes a ring-like pole piece 26A and anexciting winding 26B and which produces a generally axial magnetic fieldin the vicinity of the electrode 20. A magnet potential supply 28provides current for driving the exciting winding 26B. The pole-piece26A, which is here shown in section, has a pole tip for directing fluxat the opening between the electrode 20B and the wire stock 10 beingtreated. The steel holder is provided to assist in shaping the magneticfield from the magnet 26, so that the most concentrated flux regionexists across the small-diameter portion 24A of the electrode, and aless concentrated flux region exists across the large-diameter portion24C of the electrode. The reason for establishing this flux field inthis manner is to partially counteract the viscous effect on the arm byestablishing a field of greater energy density in the direction ofmovement of the arc than exists in the region where the arc is to bemaintained. The arc will, of course, tend to move to the region ofminimum energy density.

For initiating a plasma arc, there is provided an arc striking-powersupply 30, which can comprise any source of high potential, which, whenapplied between the electrode 20 and the conductive rollers 14 to whichthe source of potential is connected, will cause a spark to be initiatedbetween the electrode 20 and the conductive stock 10. As soon as thisspark has been struck, a power arc develops which is maintained by adirect-current power supply, here designated as thearc-sustaining-potential source 32, which is also connected between theelectrode 20 and the rollers 14. The arc-striking-power supply isautomatically turned off when the arc is ignited by any suitable meanswell known in the art, such as apparatus for sensing when a current flowis initiated by virtue of the arc being created.

Either a high-potential D.C. supply may be employed for striking thearc` or a high-potential A.C. supply. In an embodiment of the inventionwhich was built, the arcstriking-potential source was A.C. and wascoupled in series with the arc-sustaining-potential supply by thesecondary winding of an output transformer 31 having a capacitor 33connected thereacross. The arc-sustainingpotential supply may be anysupply for providing suicient current to maintain the arc. A weldingsupply was employed in an embodiment of the invention which was builtwhich provided 400 amperes current across the 45- volt drop existing inthe circuit when the arc was struck.

In an embodiment of the invention which was built, the atmospheric airprovided the gas which is necessary for a plasma arc. This should not beconstrued as a limitation upon the invention, since, if desired, any ofthe other well-known gases, such as argon or helium, may be employed.

It was previously stated that because of the cathode effect or viscouseffect, an arc which terminates on a moving electrode will be drawn inthe direction of motion of the electrode until it is extinguished. Thearrangement shown in the drawing overcomes this effect, rst, because ofthe shape of the magnetic field provided by the magnet 26 which tends todirect the plasma arc in a direction opposed to the direction of motionof the elongated conducting stock, and, second, because of the shape ofthe central aperture of the electrode 20. As a result, of this shape, anautomatic gas-pumping action occurs, and the arc is pushed as a resultof this gas-pumping action in a direction to counteract the viscouseffect. Since the orifice presented in the portion 24A of the centralopening is smaller than the orifice presented in the portion 24C of thecentral opening, a type of ram-jet effect is created, wherein the gas orair is inspirated through the small-diameter opening, is heated due tothe presence of the plasma arc, and then an incandescent gas isexhausted through the large-diameter portion 24C of the central opening.This helps to stabilize the left side of the plasma arc by presenting acold, nonionized barrier. This also serves to continually purge theplasma arc of generated impurities, thereby further enhancingstabilization. The plasma arc represented by the lines 34, once struck,tends to maintain itself between the electrode at the wide-diameterportion 24C and the stock 10.

At the second heat-applying location, an arrangement for applying aplasma arc to the stock includes two ring electrodes 40, 42, which arehere shown in section. In an embodiment of the invention which wasbuilt, these ring electrodes were made of copper and each had anaperture therein, respectively 40A, 42A, for the purpose of permittingthe circulation of a coolant, such as water. The ring electrodes 40, 42,each have at the surface opposing the other electrode and near thecentral aperture portion a protuberance, respectively 44, 46. Theseprotuberances 44, 46, oppose one another, and the opposing surfaces areflattened. The pair of ring electrodes 40, 42, are spaced quite close toone another in the region of these protuberances.

There is provided for the electrode 40 an arc-strikingpotential supply48 which has an output transformer 49. The secondary winding isresonated by a capacitor 51. The secondary winding is connected throughan arc-sustaining-potential source 50 between the electrode 40 and theconductive rollers 14. There is provided an arcstriking-power supply 52,which has an output transformer 55. The secondary winding is resonatedby a capacitor 53. The secondary winding is connected between theelectrode 42 and the roller 16 through an arc-sustainingpotential supplysource 54. In addition, there is provided at the second scavenginglocation a magnet 56 with its magnet-potential supply 58 and with itsring-like pole piece 56A, having the tips adjacent the electrode 42shaped to form an axial magnetic eld within the electrode apertures andto concentrate the flux at the space between the workpiece or conductivestock and the electrode 42.

The funnel-shaped flux pattern produced by the magnet 56 serves tooppose any tendency of the plasma arc, which is struck by employing therespective arc-strikingpower supplies 52 and 48 and which is maintainedby the respective arc-sustaining-potential supplies 50 and 54, frommoving in the direction of motion of the stock 10. The gas employed inthe embodiment of the invention which was built was atmospheric air;however, as previously explained, any of the other well-known gases,such as argon, nitrogen, or hydrogen, may be employed instead. Becauseof the shape of the electrodes and their positioning, a furtherstabilizing effect on the plasma arc, here represented by the line 60,is provided. The arc is maintained in the region shown between theelectrodes 40, 42 and the stock 10. The gas is drawn or inspiratedthrough the central aperture of the electrode 40 from the upstream side,and through the central aperture of the electrode 42 from the downstreamside. Thus, there is an opposite and balancing pressure on the arc 60.The gas is heated in the arc and then exhausted in the space between theelectrodes, thereby purging the plasma of any impurities.

It is preferred that the arc-sustaining-potential supplies 50 and 54provide an equal potential to the electrodes 40, 42. In an embodiment ofthe invention which was built, wire rod was treated while being moved ata rate on the order of 200 feet per minute. The arcsustaining-potentialsupplies 50 and S4 each provided 250 amperes across a 40-volt drop. Itshould be noted that the stock need not be round, but can have any otherstock shape and can also, for example, comprise pipe stock. Furthermore,if desired, other materials may be fed into the arc to be plated 0rdeposited on the rod. It should also be noted that because of the equaland opposite current flow between the conductive roller 14 through thestock 10 and through the arc and the conductive roller 16 through thestock 10 and through the arc the magnetic pressure effect due to currentflowing through the workpiece is cancelled.

The plasma arc created in the ring electrodes is a continuously rotatingone, rotation being due to the inner action of the axial magnetic fieldand the magnetic field created by the flow of current through the arc,which extrts a force on the arc in a direction so as to cause it torotate around the stock at the center, thereby treating the entire outersurface of the stock as it is being pulled through the ring electrode.It is preferable to make the stock negative and the electrode positive,as shown in the drawing. Although the arrangement can operate with thepolarities reversed, it is believed that a superior operation occurswith the arrangement as shown. Further, the arrangement may be operatedusing an alternating-current arc-sustaining-potential supply, ifdesired. As previously pointed out, the rise in temperature of theconductive stock, due to the arc and the current flow therethrough, maybe effectively controlled by the rate at which the stock is pulledthrough the arc. Furthermore, the current flow through the stock, in apath which may be traced from the power supply through the electrodewhich applies plasma through the plasma arc, through the stock, andthrough a roller electrode back to the power supply, provides anothercontrol over the heating and/or heat treatment of the stock. This may beachieved by varying the spacing between a roller electrode and theplasma-applying electrode. This has the effect of determining how longcurrent will flow through the stock at a given rate of speed. Obviously,the longer the amount of time which the current ows through the stock,which is established by the spacing between the roller electrode and theplasma-applying electrode, the greater the heating effect due to thecurrent flow through the stock. Thus, this invention provides a methodand means of heating the stock for heat treatment, if desired, as wellas for scavenging.

In the electrode and pickoff roller arrangement shown in FIGURE 1,current flows in the wire 10 between the plasma arc at 60 and pickotroller 16, also between plasma arc 60 and roller 14, and also betweenthe arc of the electrode 20 and the roller 14. By varying the distancebetween the rollers 16 and the electrodes, the length of current pathand thereby the time (since the wire is always moving through theelectrodes) during which the wire stock is heated by the current, isvaried.

The distance between roller 16 and electrodes 40, 42, can determine thepreheat time for the wire stock, the distance between electrode 40 androllers 14 as well as the distance between rollers 14 and electrode 20can determine the heating time for the stock.

Reference is now made to FIGURE 2 which shows an arrangement for usingthe invention for heat treating stock in addition to cleaning orstripping it. In order to simplify the showing the power supply isomitted from FIG- URE 2. The electrode 70 which provides the plasma arcas described previously, may have its position altered from the positionrepresented by the dotted rectangle 70A to the position represented bythe dotted rectangle 70B. The electrode is supported by an overheadtrolley 72, which rolls on a suitable track structure 74. The pickoffroller electrodes 76, 78, through which a connection is made through thestock back to the source of operating potential, are also attached tothe overhead support 74, on which the trolley 72 rolls. Of course, thesupport for the rollers and the plasma generating electrode 70, are allby suitable insulating structures. The rollers may also be made movable,by sliding their support attachment along the overhead support.

In accordance with the foregoing description, the plasma electrode 70will establish an arc to the stock 10. Current ows in that arc throughthe stock 10 to both pickol electrodes 76 and 78. Therefore, with thedirection of strip represented by the arrows in FIGURE 2 heat due to 12Rloss is applied to the stock before it reaches the cleaning plasma arc70 as well as afterwards. The length of time at which the stock ispre-heat treated and the length of time in which it is heat treatedafter leaving the arc, is determined by the relative position of theelectrode 70 to the pickup roller 76, as well as to the pickup roller78. Placing the electrode at 70A puts more current and thus more heatinto the entering or cold section of the stock. At the other side of theelectrode, the remaining stock section is a temperature hold sectionwith a lower current because of higher path resistance, because oflonger wire length. This section however, permits a time at temperaturemetallurgical transformation to take place. With the electrode 70, arising temperature will occur over the path length between electrode 70and roller 78. With the electrode at 70B, the greatest heating effectoccurs between 70B and 78.

FIGURE 3 shows an arrangement for effectuating the heat treatmentbetween the two spaced electrodes 80, 82. In the arrangement shown inFIGURE 3, the positions of the electrodes 80, 82, are movable since bothare supported by overhead trolleys 84, 86, which are movable. The sourceof operating potential 88, may be a center tapped power supply which isconnected to the two plasma electrodes 80, 82. Accordingly, theprincipal current path through the stock 10 is defined by the distancebetween the two plasma electrodes 80, 82. There is a preheat treatmentgiven over the path length between roller 79 and electrode 80. The maincurrent path exists between the two electrodes 80, 82, and heatingoccurs over this distance. By moving roller electrode 83, closer to orfurther from electrode 82, the temperature reached by the wire may bemaintained, increased or gradually lowered, since the relative spacingof these electrodes varies the resistance in the shunt current path (inshunt with the current path between 79 and 82) and therefore varies theamount of current flowing, accordingly.

FIGURE 4A and FIGURE 4B illustrate arrangements for etectuating heattreatment while cleaning the stock in those locations where the stock isgiven a circular path. This path is usually a vertical one and is doneto save oor space. The movement of the stock is indicated by the arrowspresent thereon. This arrangement is usually known in the trade as aVertical Hot Loop operation. The idlers, or pulleys, 92, 94, are notinvolved in the electrical circuitry. They are adjustable in order tomake the loop formed by the stock larger or smaller. The power supply96, applies current to the electrode 90 and to the electrical pickottroller 98. Therefore, the current path through the stock 10 isdetermined by the distance between the electrode 90 and the rollers 98,which in turn is determined by the size of the loop which the idlers 90,92, created by their position relative to the position of the rollers98.

FIGURE 4B illustrates the use of the vertical loop when twoV electrodes100, 102 are employed. In this case, neither of the rollers 104, 106,are involved in the electrical circuitry. The power supply 108 appliespotential with relative opposite polarity to the electrodes 100, 102,whereby a plasma arc may be struck to the wire stock 10. The electrode104 is adjustable to increase or decrease the size of loop whereby theamount of wire which extends around the electrode 104 and is in thecurrent path between the electrodes 100, 102, may be varied.

FIGURE 5 shows an arrangement for pre-heating the stock 10, thenexposing it to the plasma arc, and then quenching it. The electrode 110,establishes two current paths, one current path extends through thestock to the roller 112, the other path extends from electrode 110 toroller 116. Accordingly, due to the current ow through the wire stock10, the wire is heated in the path up to the electrode 110. As the strippasses through the electrode 110 it is also heated and cleansed by theplasma arc. The stock is then quenched in a suitable cooling arrangementas by the tank 114. The quench there may be full, partial, orinterrupted, depending upon the wishes of the user of the system. Thestock 10, then passes on to be either held at a required temperature fora second heat treatment or may be allowed to cool further, as determinedby the relative spacing of rollers 112, 116 and the plasma electrode110.

Should the heat treatment of the wire stock cause it to sag or becomeweak so that the usual pulling of the wire through the rollers andelectrodes may damage the wire, then it may be necessary to drive theroller to carry the Wire through the electrodes. Also, if desired, thewire stock may be made to pass through a pipe, as represented by thedotted lines 118, between pick-off rollers and electrodes through whicha suitable reducing gas may be passed, if it is desired to maintain aproper reducing atmosphere during the heat treatment.

There has accordingly been described and shown herein a novel, usefuland unique arrangement for effectuating heat treatment of metal stockusing an electrode arrangement which applies a plasma arc to the stock.

I claim:

1. In apparatus for cleansing the surface of elongated conductive stockwherein an electrode through which said stock moves is provided forestablishing a plasma arc therebetween by application of potential tosaid electrode and to a current pick off electrode positioned at saidconductive stock spaced from the position of said electrode, theimprovement in said apparatus for controlling the heat treatment of saidstock comprising means for adjusting the relative spacing of saidelectrode and said pickotl electrode to one another to adjust theelectrical current flow path length through said stock to therebycontrol the heat treatment of said stock.

2. In apparatus for cleansing the surface of elongated conductive stockwherein an electrode through which said stock moves is provided forestablishing a plasma arc therebetween by application of potential tosaid electrode and to a current pick off electrode positioned at saidconductive stock spaced from the position of said electrode, theimprovement in said apparatus for controlling the heat treatment of saidstock comprising means for movably supporting said electrode for motionalong said conductive stock, andv means for movably supporting saidpicko electrode for motion along said conductive stock whereby a desiredheat treatment of said stock is electuated by moving said electrode andsaid pickoff electrode to establish a current path through said stockwhich eiectuates the desired heat treatment.

3. In apparatus for cleansing the surface of elongated conductive stockwherein an electrode through which said stock may pass is provided forestablishing a plasma arc therebetween by application of potentialacross said electrode and two current picko electrodes positioned atsaid stock and one on each side of said electrode, the improvement insaid apparatus for controlling the heat treatment of said stockcomprising means for supporting said electrode to be movable along saidconductive stock for effectuating a predetermined heat treatment of saidstock by the position to which said electrode is moved relative to saidpickof electrodes.

4. In apparatus as recited in claim 3 wherein each said pickol electrodeincludes means for movably supporting said pickot electrode foradjusting its position relative to said electrode.

5. Apparatus for heat treating elongated conductive stock comprising anelectrode through which said elongated conductive stock may be passed, aconductive roller in contact with said elongated stock spaced from saidelectrode, means for applying potential between said electrode and saidconductive roller to establish a plasma arc between said electrode andsaid elongated stock, means for moving said elongated stock through saidelectrode while maintaining said plasma arc, and means for adjusting thespacing between said conductive roller and said electrode to adjustcurrent path length to effectuate a desired amount of heat treatment tothe elongated stock therebetween.

6. Apparatus for heating treating elongated conductive stock comprisinga plurality of roller means positioned for guiding said conductive stockin a loop, at least one of said roller means being conductive, anelectrode through which said conductive stock may pass positioned atsaid conductive stock which is within said loop, means for applyingpotential between said electrode and said conductive roller means toestablish a plasma arc between said electrode and said elongated stock,means for moving said elongated stock through said electrode in saidloop While maintaining said plasma arc, and means for moving said rollermeans for varying the loop size and thereby the length of stockextending between said electrode and conductive roller means to therebydetermine the heat treatment received by said conductive stock.

7. Apparatus for cleansing and heat treating wire stock comprising afirst and second electrode through which said Wire stock may pass, meansfor movably supporting said electrodes for adjusting the relativespacing therebetween along said wire stock, a rst pickoi rollerpositioned along said wire stock adjacent said Iirst electrode, a secondpickoff roller positioned along said wire stock adjacent said secondelectrode, means for supporting said rst pickoif roller to enableadjusting the spacing thereof from said rst electrode, means forsupporting said second pickoff roller to enable adjusting the spacingthereof from said second electrode, means for moving said wire stockthrough said rollers and electrodes, and means for applying potential tosaid electrodes and said pickot rollers to establish plasma arcs betweensaid electrodes and said wire stock for cleansing the surface thereofand to cause current to flow through said wire stock between the plasmaarc positions and said electrodes for affording heat treatment of saidwire stock.

8. Apparatus for scavenging the surface of elongated conductive stockcomprising means establishing a scavenging location, means for passingsaid elongated conductive stock through said scavenging location, andmeans for establishing a rotating plasma arc terminating on the surfacesof said elongated conductive stock as it is passed through saidscavenging location.

9. Apparatus for treating the surface of elongated conductive stock witha plasma arc comprising an electrode through which said elongatedconductive stock may be passed, means for establishing a plasma arcbetween said electrode and said elongated conductive stock, and meansfor moving said elongated conductive stock through said electrode whilemaintaining said plasma arc for obtaining treatment of the surfacethereof.

10. Apparatus for blasting the surface of elongated conductive stockwith high-energy ions comprising an electrode having an aperturetherethrough, means for moving said elongated conductive stock throughsaid electrode aperture, and means for establishing a rotating plasmaarc between said electrode and said elongated conductive stock forblasting the surface thereof.

11. Apparatus as recited in claim l() wherein the aperture of saidelectrode is shaped to counteract the viscous effect on said rotatingplasma arc caused by motion of said elongated conductive stock throughsaid aperture.

12. Apparatus as recited in claim wherein said electrode comprises aconductive cylinder, said aperture has a rst diameter continuing fromone end inward for a portion of said cylinder, a second diameter largerthan said first diameter continuing inward from the other end of saidcylinder for a portion of said cylinder larger than said first diameterportion, and a transition region between said rst and second diameterportions.

13. Apparatus for scavenging elongated conductive stock comprising aplurality of electrodes spaced from one another, said electrodes eachhaving apertures through which said elongated conductive stock may pass,means for passing said elongated conductive stock successively throughsaid plurality of spaced electrodes, means for establishing a rotatingplasma arc between each of said electrodes and said elongated conductivestock as it is passed through said spaced electrodes for blasting thesurface thereof, and means positioned adjacent each plasma arc foropposing any viscous effects due to motion of said conductive stock.

14. Apparatus for scavenging as recited in claim 13 wherein said meansfor passing said elongated conductive stock successively through saidplurality of spaced electrodes includes a plurality of conductiverollers for movably supporting said stock, and said means forestablishing a rotating plasma arc between each of said electrodes andsaid elongated conductive stock includes a separate source of operatingpotential connected between an electrode and a roller and means forestablishing a magnetic ield along said conductive stock.

l5. Apparatus for scavenging as recited in claim 12 wherein two of saidplurality of spaced electrodes are placed sutliciently close to oneanother for achieving gas inspiration from opposite directions with anexhaust gas flow therebetween and to achieve cancellation of themagnetic pressure effect caused by the currents flowing in theconductive stock.

16. Apparatus for scavenging as recited in claim 13 wherein said meanspositioned adjacent each plasma arc for opposing any viscous eiects dueto motion of said conductive stock includes a ring magnet having acentral aperture through which said conductive stock passes, said ringmagnet being positioned adjacent an electrode and having its pole pieceshaped for forming a region of greater flux concentration in the regionadjacent said arc in the direction of stock movement than in the regionof an electrode in which an arc is established.

17. Apparatus for treating elongated conductive stock with high-energyions comprising a pair of cylindrical electrodes each having a centralaperture through which said stock may be passed, said cylindricalelectrodes being positioned adjacent one another with their centralapertures aligned, each said electrode having on the side facing theother electrode and near the central aperture a raised flattenedprotuberance, said protuberances opposing each other, a conductive meanspositioned on either side of said pair of circular electrodes forsupporting said elongated stock for passage through said pair ofelectrodes, a means connected between an electrode and a conductivemeans for establishing a plasma arc between each of said electrodes andsaid elongated conductive stock, and means positioned adjacent the oneof said pair of electrodes on the downstream side of said pair ofelectrodes for providing a magnetic eld to oppose any viscous effect onsaid plasma arc.

18. Apparatus for treating elongated conductive stock with a plasma arccomprising a plurality of cylindrical electrodes each having a centercavity through which said stock may be passed, one of said cylindricalelectrodes having a center cavity with two dimensions one of which issmaller than the other, there being a gradual transitional regionbetween said two cavity dimensions, the portion of said cavity havingthe smaller cavity being on the trailing-edge side of said electroderelative to motion of said conductive stock therethrough, a pair of saidplurality of cylindrical electrodes being positioned adjacent oneanother with their central apertures aligned, each of said pair ofelectrodes having on the side facing the other electrode and near thecentral aperture a raised attened protuberance, said protuberancesopposing each other, rst conductive roller means for supporting saidconductive stock positioned between said one electrode and said pair ofelectrodes, second conductive roller means for supporting saidconductive stock positioned on the side of said pair of electrodesfurtherest away from said first conductive roller means, tirst means forestablishing a plasma arc between said conductive stock and said oneelectrode connected between said one electrode and said first conductiveroller means, second means for establishing a plasma arc between saidconductive stock and one of said pair of electrodes connected betweensaid one of said pair of electrodes and said first conductive rollermeans, and third means for establishing a plasma arc between saidconductive stock and the other of said pairs of electrodes connectedbetween said other of said pair of electrodes and said second conductiveroller means.

19. Apparatus as recited in claim 18 wherein there is provided for eachsaid one electrode and for said pair of electrodes and positioned on thedownstream side thereof a magnetic means for opposing any viscouseffects due to motion of said conductive stock, each of said magneticmeans having a ring magnet with a central aperture through which saidstock may pass, the pole piece of said ring magnet being shaped forforming a region of greater ux concentration in the region adjacent saidarc in the direction of stock movement than in the region of theelectrode in which an arc is established.

20. An electrode structure for establishing a plasma arc comprising apair of cylindrical conductive cylinders positioned adjacent one anotherand having aligned central apertures each said cylinder having on theside facing the other cylinder and near the central aperture a raisedflattened protuberance, said protuberances opposing each other.

21. The method of scavenging the surface of wire stock comprisingestablishing a rotating plasma arc terminating on the surface of saidstock, moving said stock, and maintaining said rotating plasma are atthe location at which it is established despite motion of said stock.

22. The apparatus of claim 10 wherein said means for establishing arotating plasma arc between said electrode and said elongated conductivestock includes means for establishing a potential difference betweensaid electrode and said conductive stock and means for establishing amagnetic eld along said conductive stock.

23. The method of scavenging the surface of wire stock comprisingestablishing a plasma arc terminating on the 10 2,874,265

surface of said stock, rotating said plasma are around said stock,moving said stock, and maintaining said rotat ing plasma arc at thelocation at which it is established despite motion of said stock.

References Cited in the le of this patent UNITED STAIESJPATENTS 484,637Hunter Oct. 18, 1892 2,465,093 Hanson et al Mar. 22, 1949 Reed et alFeb. 17, 1959

1. IN APPARATUS FOR CLEANSING THE SURFACE OF ELONGATED CONDUCTIVE STOCKWHEREIN AN ELECTRODE THROUGH WHICH SAID STOCK MOVES IS PROVIDED FORESTABLISHING A PLASMA ARC THEREBETWEEN BY APPLICATION OF POTENTIAL TOSAID ELECTRODE AND TO A CURRENT PICK OFF ELECTRODE POSITIONED AT SAIDCONDUCTIVE STOCK SPACED FROM THE POSITION OF SAID ELECTRODE, THEIMPROVEMENT IN SAID APPARATUS FOR CONTROLLING THE HEAT TREATMENT OF SAIDSTOCK COMPRISING MEANS FOR ADJUSTING THE RELATIVE SPACING OF SAIDELECTRODE AND SAID PICKOFF ELECTRODE TO ONE ANOTHER TO ADJUST THEELECTRICAL CURRENT FLOW PATH LENGTH THROUGH SAID STOCK TO THEREBYCONTROL THE HEAT TREATMENT OF SAID STOCK.